BEE Bachelor of Electrical Engineering Electric Circuit Analysis Questions and Answers — Questions and Answers
Question 1: According to the superposition theorem, to find the contribution of a single current source in a linear circuit with multiple sources, all other sources must be:
- Replaced by short circuits.
- Replaced by open circuits.
- Voltage sources replaced by open circuits and current sources by short circuits.
- Voltage sources replaced by short circuits and current sources by open circuits. (Correct answer)
Correct answer: Voltage sources replaced by short circuits and current sources by open circuits.
The superposition theorem states that the response in any element of a linear circuit is the sum of the responses caused by each source acting alone. To consider one source, all other independent voltage sources are turned off (replaced by a short circuit) and all other independent current sources are turned off (replaced by an open circuit).
Question 2: A DC voltage source has a Thevenin equivalent voltage of 12V and a Thevenin equivalent resistance of 3Ω. To achieve maximum power transfer, what should be the value of the load resistance?
- 12Ω
- 6Ω
- 3Ω (Correct answer)
- 9Ω
Correct answer: 3Ω
The Maximum Power Transfer Theorem states that for a DC circuit, maximum power is delivered from a source to a load when the load resistance (RL) is equal to the Thevenin equivalent resistance (Rth) of the source. In this case, Rth is 3Ω, so RL must also be 3Ω.
Question 3: In the context of nodal analysis, what is a 'supernode' used for?
- To simplify a circuit with only current sources.
- To group all nodes connected to the ground reference.
- To handle a voltage source connected between two non-reference nodes. (Correct answer)
- To combine all parallel branches into a single equivalent branch.
Correct answer: To handle a voltage source connected between two non-reference nodes.
A supernode is formed when a voltage source (either independent or dependent) is connected between two non-reference nodes. This technique allows for the application of Kirchhoff's Current Law (KCL) to the combined supernode and requires an additional constraint equation from Kirchhoff's Voltage Law (KVL) for the voltage source itself.
Question 4: Which of the following correctly describes a Norton equivalent circuit?
- A voltage source in series with a resistor.
- A current source in parallel with a resistor. (Correct answer)
- A voltage source in parallel with a capacitor.
- A current source in series with an inductor.
Correct answer: A current source in parallel with a resistor.
Norton's theorem states that any linear electrical network can be replaced by an equivalent circuit consisting of a single current source (IN) in parallel with a single equivalent resistance (RN).
Question 5: A series RLC circuit is subjected to a step DC voltage input. If the response shows decaying oscillations before reaching a steady state, the circuit is said to be:
- Critically damped
- Overdamped
- Undamped
- Underdamped (Correct answer)
Correct answer: Underdamped
In a series RLC circuit, an underdamped response is characterized by oscillations that gradually decrease in amplitude over time until the circuit reaches its steady-state condition. This occurs when the damping factor is less than the natural frequency.
Question 6: When calculating the Thevenin equivalent resistance (Rth) for a circuit containing independent sources, what is the correct procedure?
- All voltage sources are replaced by open circuits and all current sources are replaced by short circuits.
- All sources are left active and the resistance is calculated across the output terminals.
- All voltage sources are replaced by short circuits and all current sources are replaced by open circuits. (Correct answer)
- Only voltage sources are replaced by short circuits; current sources remain active.
Correct answer: All voltage sources are replaced by short circuits and all current sources are replaced by open circuits.
To find the Thevenin equivalent resistance (Rth), all independent sources within the circuit must be deactivated. This is achieved by replacing independent voltage sources with short circuits (zero voltage) and independent current sources with open circuits (zero current).
BEE Bachelor of Electrical Engineering Electric Circuit Analysis Questions and Answers
According to the superposition theorem, to find the contribution of a single current source in a linear circuit with multiple sources, all other sources must be: